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We report detailed morphometric observations on several MIS 5.5 and a few older (MIS 11, 21, 25) fossil tidal
notches shaped along carbonate coasts at 80 sites in the central Mediterranean Sea and at an additional six sites
in the eastern and western Mediterranean. At each site, we performed precise measurements of the fossil tidal
notch (FTN) width and depth, and of the elevation of its base relative to the base of the present tidal notch (PTN).
The age of the fossil notches is obtained by correlation with biologic material associated with the notches at or
very close to the site. This material was previously dated either through radiometric analysis or by its fossiliferous
content.
The width (i.e. the difference in elevation between base and top) of the notches ranges from 1.20 to 0.38 m,
with a mean of 0.74 m. Although the FTN is always a few centimetres wider than the PTN, probably because of
the lack of the biological reef coupled with a small erosional enlargement in the FTN, the broadly comparable
width suggests that tide amplitude has not changed since MIS 5.5 times. This result can be extended to the MIS
11 features because of a comparable notch width, but not to the MIS 21 and 25 epochs. Although observational
control of these older notches is limited, we regard this result as suggesting that changes in tide amplitude
broadly occurred at the Early-Middle Pleistocene transition.
The investigated MIS 5.5 notches are located in tectonically stable coasts, compared to other sectors of the
central Mediterranean Sea where they are uplifted or subsided to ~100m and over. In these stable areas, the
elevation of the base of the MIS 5.5 notch ranges from 2.09 to 12.48 m, with a mean of 5.7 m. Such variability,
although limited, indicates that small land movements, deriving from slow crustal processes, may have occurred
in stable areas. We defined a number of sectors characterized by different geologic histories, where a careful
evaluation of local vertical land motion allowed the selection of the best representative elevation of the MIS 5.5
peak highstand for each sector. This elevation has been compared against glacial isostatic adjustment (GIA)
predictions drawn from a suite of ice-sheet models (ICE-G5, ICE-G6 and ANICE-SELEN) that are used in combination
with the same solid Earth model and mantle viscosity parameters. Results indicate that the GIA signal is
not the main cause of the observed highstand variability and that other mechanisms are needed. The GIA simulations
show that, even within the Mediterranean Basin, the maximum highstand is reached at different times
according to the geographical location. Our work shows that, besides GIA, even in areas considered tectonically
stable, additional vertical tectonic movements may occur with a magnitude that is significantly larger than the
GIA.